1. Field of the Invention
The present invention relates to bio-separation systems, and more particularly a coupler for aligning optical detection components.
2. Description of Related Art
Bioanalysis, such as DNA analysis, is rapidly making the transition from a purely scientific quest for accuracy to a routine procedure with increased, proven dependability. Medical researchers, pharmacologists, and forensic investigators all use DNA analysis in the pursuit of their tasks. Yet due to the complexity of the equipment that detects and measures DNA samples and the difficulty in preparing the samples, the existing DNA analysis procedures are often time-consuming and expensive. It is therefore desirable to reduce the size, number of parts, and cost of equipment, to ease sample handling during the process, and in general, to have a simplified, low cost, high sensitivity detector.
One type of DNA analysis instrument separates DNA molecules by relying on electrophoresis. The term electrophoresis refers to the movement of a charged molecule under the influence of an electric field. Electrophoresis can be used to separate molecules that have equivalent charge-to-mass ratios but different masses. DNA fragments are one example of such molecules. Electrophoresis techniques could be used to separate fragments of DNA for genotyping applications, including human identity testing, expression analysis, pathogen detection, mutation detection, and pharmacogenetics studies.
There are a variety of commercially available instruments applying electrophoresis to analyze DNA. One such type is a capillary electrophoresis (CE) instrument. CE instruments employ a fused silica capillary column carrying a buffer solution. A DNA sample is capable of being introduced through the capillary column by electrophoresis. When electrophoresis is applied to the capillary column, the DNA sample separates into its components, and the components migrate through the capillary column to a detection window where the DNA components can be analyzed.
There are detection techniques well known in the art for analyzing the DNA components. Radiation absorption detection is one such well-known technique that involves directing incident radiation at the analytes in the detection window and measuring the amount or intensity of radiation that passes through the analytes, or the equivalent decrease in intensity or the amount of radiation that is absorbed by the analytes (i.e., the attenuation of the incident radiation).
Another well-known detection technique is Emissive radiation detection. Fluorescence detection, such as Laser-induced fluorescence (LIF) detection methods, is often the detection method of choice in the fields of genomics and proteomics because of its outstanding sensitivity compared to other detection methods. The DNA sample is tagged with a fluorescent material. The DNA components can be analyzed by directing light through the capillary wall at the detection window, at the tagged components, and detecting the fluorescence emissions induced by the incident light. The intensities of the emission are representative of the concentration, amount and/or size of the components of the sample.
There are numerous challenges in designing CE-based instruments and CE analysis protocols. To maximize signal intensity and sensitivity and resolution of detection, the precise position and alignment of particular CE instrument components, such as the capillary column, the excitation light fiber and the detection lens, with respect to each other are critical design concerns. The capillaries used in CE are relatively small, ranging in size from 20 μm to 250 μm I.D., and CE requires that the detection window/zone be small enough to reduce the scattered background/excitation, lower the baseline Noise, increase Signal/Noise ratio and improve detection sensitivity. It is critical for the excitation fiber to be precisely positioned and aligned such that a substantial portion of the light beam is directed through the capillary wall at the separated sample components in the capillary bore. Otherwise, the light can scatter at the outside capillary wall/air interface and inside capillary wall/buffer interface (Raman scattering), which can obscure or corrupt the fluorescence emission intensity. The problem can be multiplied if more than one fiber is used. Therefore, having one or more excitation fiber positioned and aligned precisely with the detection window is desirable.
Additionally, sample size and background noise pose additional concerns in designing CE-based instruments. Only a relatively small amount of DNA sample is being analyzed at any given time. As such, the small sample emits fluorescence signals at levels that compete with background noise. The background noise can come from the light source, from Raman scattering, or from the materials of other instrument components. The fluorescence signal can also scatter at the wall interfaces. One or more lenses have been used to increase detection sensitivity. However, a small misalignment of the detection lens can have large effects on the detection sensitivity. Accordingly, it is desirable for one or more detection lens elements to be precisely positioned and aligned with the detection window. Furthermore, having instrument components made from materials that minimize background noise is desirable.
In the past, various techniques were developed for more completely collecting the fluorescence emissions to improve signal intensity and hence detection sensitivity. These techniques involved additional moving and non-moving components that added to the relative complexity and cost of the detection setup. Therefore, it is desirable to have a means for CE analyses that is versatile enough for use in a laboratory setting as well as being capable of incorporation into a CE-based instrument capable of various detection techniques. Additionally, this also calls for a means of producing and assembling instruments at low cost.